1. Field of the Invention
The present invention relates to tape automated bonding.
2. Description of the Related Art
Tape automated bonding is well known in the semiconductor industry. In conventional tape automated bonding leads, which are intended to be attached to a semiconductor chip prior to packaging the chip, are provided on a film similar to 35 mm photographic film by photolithography. The leads extend into an aperture at the center of each "frame" of the film, each frame having leads for one semiconductor chip. For example, a frame for a square chip has a square aperture and the leads extend into the aperture from all four sides of the aperture. The leads are formed of copper and are tinned so that they may be attached to solder bumps (or pads) on the chip by, e.g., reflow soldering. After the leads are attached to the chip, the leads and the chip are removed from the tape for packaging; the packaging may be plastic or ceramic encapsulation.
Advances in semiconductor manufacturing techniques have led to the ability to provide a significantly increased number of semiconductor devices per unit area. Thus, a chip of a given size has more devices and consequently more pads to which leads must be attached. When tape automated bonding is utilized to attach leads, the pads are provided around the periphery of the chip; accordingly, increasing the number of pads reduces the spacing or pitch of the pads.
As the pitch of leads for tape automated bonding is decreased, the leads must have a reduced cross-sectional area, and thus are more fragile. For dimensions currently used and for reduced dimensions of future semiconductor devices, the leads are so fragile that the processing steps utilized to fabricate the leads and subsequent handling can bend or otherwise damage the leads. Such bending or damage to the leads results in misalignment of the leads and the pads during bonding, thus making bonding difficult or impossible. The result is low yield. Conventional tape automated bonding uses approximately 300 leads/die for an 8 mm.times.8 mm die, and can be extended to 400 leads/die. However, with this number of leads per die and the lead size necessary (each lead has a minimum width of approximately 50 .mu.m) to achieve same, damage to the leads during fabrication and bonding causes too many losses. With conventional tape automated bonding the minimum lead width is 50 .mu.m and the minimum pitch is also 100 .mu.m.